Conventional Switched-capacitor Converters Research Articles

Techniques for Analyzing and Reducing Voltage Conversion Ratio Transition Losses of Capacitive DC–DC Converters for Fast-DVS-Enabled Systems

Switched-capacitor (SC) converters have numerous advantages in supplying fast and fine-grained voltages to microprocessors. However, the losses associated with the voltage conversion ratio (VCR) transition, which has not been investigated in detail, may cause a significant efficiency drop. This letter presents a simple and accurate model for estimating energy losses during the VCR transition of many-ratio SC dc–dc converters. The loss model begins with the assumption that the charge redistribution among flying and load capacitors is the leading cause for the VCR transition losses. The analysis of different types of many-ratio SC dc–dc converters shows that the model is consistent with the simulated results. For more verification, a test chip containing a converter with an algorithmic voltage-feed-in topology was fabricated in a 0.18-μm CMOS process, with the measured results also in good agreement with the model outcomes. Furthermore, to mitigate the VCR transition loss, several techniques are discussed and analyzed based on the presented model. In particular, the SC converter with flying capacitor reordering method shows 28.9% conversion efficiency improvement over the conventional SC converter with negligible circuit overhead.

Design of Monolithic All-NMOS Three-Level Three-phase Switched-Capacitor Power Converter for Industrial Environmental Sensor Conditioning

This article presents a fully integrated, high conversion ratio, three-level switched-capacitor (SC) power converter. The converter adopts a tri-mode operation in contrast to classic dual-mode operation in conventional SC converters. The unique circuit structure and operation create an inherent third power rail, which facilitates the use of low-voltage devices at high supply voltage for fast speed and low-silicon real estate. The tri-mode operation naturally matches a three-phase interleaving scheme for improved output voltage ripple and transient response. Implemented on a 0.35-μm BCD process, the design prototype accomplishes a conversion ratio greater than 4:1 and a maximum power delivery of 180 mW at 6-V input and a switching frequency of 93 MHz. With the efficient use of on-chip power switches and capacitors, it achieves a maximum power density of 125 mW/mm².

Extending the Supercapacitor-Assisted Low-Dropout Regulator (SCALDO) Technique to a Split-Rail DC–DC Converter Application

The Supercapacitor-assisted low-dropout (SCALDO) regulator is a unique new DC-DC converter design approach with high end-to-end efficiency (ETEE), where a supercapacitor is used as a lossless voltage dropper in the series path of a linear regulator. This technique, in which the energy recovery happens at a very low frequency (typically in millihertz), with an efficiency multiplication factor in the range of 1.33 to 3, can be used in many different applications. For example, in a 12- 5V linear converter where the theoretical maximum efficiency is 41.67%, the SCALDO approach improves it to 83.33%. The SCALDO technique has been extended to multiple useful applications proving its versatility and has been identified as an entirely different approach compared to conventional switched capacitor converters. In this paper, we provide an in-depth discussion on the expansion of the SCALDO technique into a dual-polarity, split-rail DC power supply with high ETEE, high current, high slew-rate capability and other desirable features. It also presents the experimental results for a 12V to ± 5V prototype with steady-state performance, transient response capability, load/line regulation, and loss estimation.

A Novel Switched-Capacitor Converter With High Voltage Gain

In this paper, a novel topology of switched-capacitor converter is proposed. Compared with the existing switched-capacitor topologies, such as the Dickson-based switched-capacitor converter or the ladder switched-capacitor converter, it limits both voltage stress and current stress of components under lower level, which reduces the volume of capacitor banks and the conduction loss. These characteristics can help high-power density and high-efficiency design, especially in high-voltage-gain applications. The phase shift modulation strategy corresponding to the proposed switched-capacitor converter is also presented in this paper. With phase shift modulation, voltage gain can be adjusted as continuous value. The voltage regulation ability makes up the defect of conventional switched-capacitor converters, and the ZVS operation of all the switching devices is also achieved with the proposed modulation method so that the WBG devices can play more strength in the converter with higher switching frequency. The derivation of the circuit topology and phase shift modulation will be introduced in this paper. The steady analysis and performance comparison will prove the advantage of the proposed converter. A 600-W prototype is built, and the experiment results are presented to validate the proposed converter.

An Energy Efficient Charging Technique for Switched Capacitor Voltage Converters With Low-Duty Ratio

Charging a capacitor array of a switched-capacitor (SC) dc-dc converter, supplying load circuits with a very short active period, can be pivotal to achieve high energy efficiency of its operation. This is because the capacitors may lose most of the stored energy during a long sleep period, and thus every sleep-to-active transition requires full recharging of the capacitors. In this brief, we present an energy efficient capacitor charging technique called split-capacitor charging, which charges a capacitor array in a step-wise fashion. Circuit simulations demonstrate that the proposed technique can reduce the energy wastage during sleep-to-active transition up to 66%. When tested on load circuits with a short active period, a voltage converter employing the proposed charging method shows up to 24% improvement in energy efficiency over conventional SC converters.

Step-Up Switched-Capacitor Quasi-Resonant Converter With Continuous Conversion Ratio

Inherent disadvantages of conventional switched-capacitor converters (SCCs) are their discrete conversion ratio and inefficient energy transfer. To overcome these downsides, a switched-capacitor quasi-resonant pulsewidth-modulated converter is proposed. The operation stages and steady-state characteristics are described. Besides the theoretical analysis, experimental results for a step-up SCC are presented. The efficiency of this 100-W converter varies between 87% and 96% over a 30–40 V input voltage range with the output voltage between 80 and 160 V.

A Reconfigurable Voltage Converter With Split-Capacitor Charging and Energy Recycling for Ultra-Low-Power Applications

This paper presents a reconfigurable on-chip switched capacitor (SC) voltage converter aimed at ultra-low- power applications. The proposed voltage converter provides an additive advantage of energy saving during both sleep-to-active and active-to-sleep transitions. This is done by incorporating two techniques, so called, split-capacitor charging (step-wise charging), and energy recycling. Split-capacitor charging is proved to reduce the energy loss during the sleep-to-active transition by 66%. An existing symmetric energy recycling technique recovers 75% of the energy from the capacitor bank at the expense of a large-output voltage ripple. In this paper, an improved method called asymmetric energy recycling reconfiguration (s) is introduced. The asymmetric energy recycling reduces the output voltage ripple by 50% compared with the symmetric recycling technique, without sacrificing the recycling efficiency. It can salvage 75.42% of the capacitor energy in active-to-sleep transition that would have been wasted through leakages during a long sleep period. Circuit simulations of the proposed SC voltage converter demonstrate up to 23.13% improvement in energy efficiency compared with conventional SC converters for a short active period.

High‐gain soft‐switching interleaved switched‐capacitor DC–DC converter with phase‐shedding technique

This study experimentally verifies the performance of a high-gain soft-switching interleaved switched-capacitor (ISC) DC–DC converter based on phase-shedding technique. Efficiency improvement especially under light load condition is achieved by introducing the phase-shedding technique, which adjusts the number of active interleaved converters based on the input power level. The interleaved configuration and modular characteristic of the converter increase the voltage gain as well as the current rating of the converter. Moreover, pulsating input current issue of conventional switched-capacitor converter is solved by the stray inductances distributed in the converter. The converter achieves high-voltage gain, improved efficiency, magnetic components free design and low output capacitance requirement. Simulation and experimental results taken from 1.5 kW prototype operating at 120 kHz are documented in this study to validate the operation and characteristics of the proposed ISC DC–DC converter.

Flying-Domain DC–DC Power Conversion

This paper presents a new power conversion method that can achieve both high efficiency and high power density by obviating the need for an area-consuming flying capacitor and replacing it with a flying digital load. The proposed flying-domain (FD) power conversion concept enables higher conversion efficiency than a conventional switched-capacitor converter by reducing charge-sharing and bottom-plate parasitic losses, while also enabling higher power density by eliminating the area occupied by the flying passive itself. This paper presents state-space analysis that shows that the proposed FD concept is well posed and reaches a valid steady state, while also presenting experimental results of several FD converters implemented in 180 nm SOI. With no flying passives, the fabricated FD converter achieves a peak efficiency of 99.2%, delivers up to 11.8 W/mm2 (2.3 W/mm2 with decoupling) at 91.7% efficiency, and can directly power a cofabricated Cortex M0 processor that communicates via flying I/O level shifters.

A General Method for Analyzing Resonant and Soft-Charging Operation of Switched-Capacitor Converters

Traditionally, switched-capacitor (SC) converters have suffered from high transient currents, which limit both the efficiency and power density of such converters. Soft-charging operation can be employed to eliminate the current transients and greatly improve the power density of SC converters. In this approach, a second-stage magnetic converter is cascaded with the SC stage to act as a controlled current load. Another approach is to use resonant SC converters with zero-current switching. This paper shows that resonant and soft-charging operations of SC converters are closely related, and a technique will be proposed, which achieves either operation by adding a single inductor to existing SC topologies. In addition, since most preexisting resonant or soft-charging SC converters were devised in an ad-hoc manner, this paper formulates an analytical method that can determine whether an existing conventional SC converter topology is compatible with the proposed approach. A number of common SC topologies are analyzed, including Dickson, series-parallel, ladder, Fibonacci, and doubler configurations. Through comparison to simulated results, as well as experimental work, the proposed method is validated and a family of high-performance SC converters is obtained.

A Fast Transient Response Flying-Capacitor Buck-Boost Converter Utilizing Pseudocurrent Dynamic Acceleration Techniques

A fast transient response flying-capacitor buck-boost converter is proposed to improve the efficiency of conventional switched-capacitor converters. The voltage boost ratio of the proposed converter is 2D, where D is the duty cycle of the switching signal waveform. Furthermore, the proposed structure utilizes pseudocurrent dynamic acceleration techniques to achieve fast transient response when load changes between heavy load and light load. The switching frequency of the proposed converter is 1 MHz for 3.3-V input and 1.0-4.5-V output range application. Experiment results show that the proposed scheme improves the transient response to within 2 μs and the total power conversion efficiency can be as high as 89.66%. The proposed converter has been realized by a 2P4M CMOS chip by 0.35-μm fabrication process with total chip size of about 1.5 mm × 1.5 mm, PADs included.

Microprocessor‐conducted noise reduction with switched supercapacitors

Microprocessors inject noise into the power distribution network (PDN). The point-of-load (PoL) converters are preferred for microprocessor supplies to reduce the total number of supplies. In addition, PoL helps in reducing voltage drop and power loss, and leverages the PDN impedance requirements by sending power at higher voltage and stepping down at the required location. Switched capacitor converters (SCCs) are replacing inductor-dominated buck converters in PoL applications because of their potential to integrate with microprocessors. A new method to reduce microprocessor-conducted noise by switched supercapacitors built with a 1:1 SCC is proposed. The high-frequency microprocessor noise conducted into the PDN is reduced by the capacitors switching at low frequency. An analogue implementation of the individual switches with low noise coupling through parasitic capacitance and with current limiting is shown. An insertion loss of 40–20 dB in the conducted frequency range (150 kHz–30 MHz) is observed in experiments. The idea can be used as a standalone method or can be incorporated into conventional SCCs with modifications as an additional feature.

High-Performance Bridge Modular Switched-Capacitor Converter With Small Component Requirement Based on Output Impedance Analysis for Low Loss

In this paper, a novel multilevel bridge modular switched-capacitor converter is proposed for the application in high voltage gain. Compared with the conventional switched-capacitor converters, it utilizes fewer components (switching device and capacitor) to obtain the same voltage conversion, as well as some advantages including low total power device rating, output capacitor requirement, and low output voltage ripple. In order to illustrate its superiority, an output impedance analysis method is developed, which can comprehensively evaluate a two-phase switched-capacitor converter's steady-state performance by judging its output impedance. The simple formulation developed not only permits optimization of the capacitor sizes to meet several constraints such as a total capacitance or total energy storage limit, but also permits optimization of the switch sizes subject to constraints on total switch conductance or total switch volt-ampere products. Consequently, the output impedance under the optimizations has contributed to the comparison of the latest switched-capacitor converters. As a result, the performance (based on conduction loss) of the proposed converter is proved to be optimum in fast-switching-limit impedance and does well in slow-switching-limit output impedance as well. Simulation and experimental results have validated the principle and properties of this converter and the analysis method.

Switched-capacitor bi-directional converter performance comparison with and without quasi-resonant zero-current switching

The proposed quasi-resonant (QR) zero-current switching (ZCS) switched-capacitor (SC) converter is a new type of bi-directional power flow control conversion scheme. This device provides voltage conversion ratios from 2 against 1/2 (double-mode/half-mode) to n against 1/n (n-mode/1/n-mode) by adding a different number of SCs and power multi-oxide-semiconductor field-effect-transistor (MOSFET) switches with a small series-connected resonant inductor for forward and reverse schemes. The proposed QR SC converter presents low current stress and balanced resonant current advantages. The operating principle and theoretical analysis of the proposed bi-directional power conversion scheme are described in detail with circuit model analysis. The proposed device is compared with the conventional SC converter. Simulations and experimental verification are carried out to verify and compare the proposed QR ZCS SC bi-directional converter performance with the conventional device. At maximum efficiency, the proposed device can achieve 96% and 93% for the forward and reverse power flow control schemes, respectively.

Generalised analysis of switched-capacitor step-down quasi-resonant converter

Conventional switched-capacitor converter circuits have a high current stress because of the short circuit when charging and discharging the capacitors. A novel switched-capacitor quasi-resonant step-down converter family with a generalised analysis that can improve the current stress problem is presented. Measured efficiency is high and all the circuits can operate under zero-current switching.

Zero-current switching switched-capacitor quasiresonant step-down converter

Current stress is usually high for conventional switched-capacitor converter circuits, because of short-circuiting when charging up the capacitors. In this paper, two zero-current switching switched-capacitor resonant step-down converter families are presented which can improve the current stress problem. They are able to provide 1/2 to 1/n, and −1 to −1/n conversion ratios respectively by using only two switches. Principles of operation, computer simulation and experimental results of the proposed converters are presented. The measured efficiency is high and all parts of the circuits are under zero-current switching conditions.